U.S. Published Patent Application No. 2010/0020646 describes an ultrasonic transducer, which provides a transmission path between an oscillating surface (piezoelectric ceramic) of the transducer material and a medium in which the oscillations are transmitted, a so-called λ/2 resonator (thickness mode transducer) including an essentially rod-shaped transmission element, which is variable in shape, length and cross section, being mentioned. However, the preferred length of the transmission element is in particular λ/4. The design of the transmission element depends on the acoustic radiation pattern to be achieved at the resonance frequency. In one specific embodiment, the transmission element is integrated into a protective housing of the sound transducer.
Proceeding from the piezoelectric ultrasonic transducer described in U.S. Published Patent Application No. 2010/0020646, which includes a forward and a rear transmission element, U.S. Pat. No. 8,320,218 describes an ultrasonic transducer which is hidden, for example in a bumper, in conjunction with parking systems. The forward, rod-shaped transmission element is designed as a composite element, further including a smooth plate, for example a portion of the material surface (bumper, vehicle door), on which the ultrasonic transducer is installed in a hidden manner. This smooth area is part of the resonator structure and is excited by the electroacoustic transducer.
Furthermore, means are described for a hidden and protected installation of the ultrasonic transducer.
German Published Patent Application No. 10 2009 040 264 describes an elongated ultrasonic transducer, which is coupled to a component of a vehicle in such a way that a longitudinal axis of the ultrasonic transducer is essentially coupled perpendicularly to an area of the component, local thickness mode oscillations of the component being caused in an active ultrasonic transducer to generate ultrasonic waves. In this way, an improved radiation pattern of the ultrasonic lobe may be achieved and a hidden installation may be implemented.
German Published Patent Application No. 10 2009 040 264 relates to an elongated ultrasonic transducer having a larger length dimension than the width dimension, which may be composed of multiple disks, designed as a monolithic piezoceramic or as a rod-shaped piezo element.